Assembly including a pressure sensor, with an activation module, and a microprocessor for measurement and control purposes

ABSTRACT

A tire pressure assembly includes a tire pressure sensor for automobile vehicle wheels and a microprocessor for pressure measurement and for control of a radio transmission circuit. The sensor has a module for activating the microprocessor associated with an activation control timer. The timer is programmable and the assembly includes means for programming the timer.

BACKGROUND

The present application relates to pressure sensors for the tires ofautomobile vehicles.

In order to ensure the safety of automobile vehicles, their tires arefitted with pressure sensors connected by radio to the on-board computerin order to signal any fault. The sensor housed inside the tire ispowered by a battery. In order to retain the autonomy of the battery ofthe sensor, which is inaccessible, this sensor operates only in acyclical manner, i.e. it has a timing circuit, for activation purposes,which has a very low power consumption and which cyclically activates amicroprocessor for a short period, this microprocessor measuring thepressure and temperature and transmitting these measurements by radio.

A wheel rim carrying the sensor can reach high temperatures in the caseof repeated intense braking and the microprocessor of the sensor is thusheated to a temperature of about one hundred degrees Celsius.

This temperature exceeds the limit at which industrial standardintegrated circuits can be guaranteed to operate properly. There aremilitary standard integrated circuits with a wider operating temperaturerange but they are naturally more expensive.

A solution has therefore been required to avoid the risk of the thermaldestruction of the circuits by operation outside their thermal range.

An earlier solution presented in the application FR 00 12 657 proposes atire pressure sensor for an automobile vehicle having a module foractivating a microprocessor for measuring and controlling radiotransmission circuits and temperature-sensitive inhibiting means toinhibit the activation module. This solution consists of using theactivation module as a switch for the operation of the microprocessor sothat cyclical operation takes place only if the temperature does notexceed a specific threshold.

The major disadvantage of this system is derived from the difficulty inregulating the threshold and the period of the cycle in dependence,principally, upon the integrated circuits used, the specifications ofthe manufacturers and assembly and/or usage adjustments.

Furthermore, automobile vehicles are assembled on automatic vehicleassembly lines which include a manual step of teaching the vehicle'son-board computer the identification numbers of the wheels and theircorresponding location on the vehicle. This manual operation is normallycarried out at a diagnostic station integrated into the vehicle assemblyline and wheel assembly line for these vehicles, taking into account thefact that a precise location of the wheel on the vehicle corresponds tothe position of a wheel in the wheel assembly line.

SUMMARY

The applicant has also sought to cause the pressure sensors to permitautomation of this step of teaching the identification of the sensorsand location of the corresponding wheels in the on-board computer of thecorresponding vehicle.

The applicant has in the first place sought to overcome the difficultyin control while improving the operation of the sensor withoutincreasing the cost thereof.

More precisely, the applicant has sought to propose a pressure sensorwhich is adjustable and compatible with the high rate of wheel andvehicle assembly on their respective assembly lines.

To this end one embodiment relates to an assembly including a tirepressure sensor for automobile vehicle wheels and a microprocessor forpressure measurement and for control of a radio transmission circuit,the sensor having a module for activating the microprocessor associatedwith an activation control timer, characterized in that the timer isprogrammable and means are provided for programming it.

In some embodiments it is possible to dispense with the use of athreshold to control the operation of the activation module by directlymodulating the rate of activation of the microprocessor by a program.

The microprocessor is preferably arranged to program the timer.

In some embodiments, the means necessary for activation of themicroprocessor are located in the microprocessor itself.

In a first embodiment the timer is mounted in the pressure sensor and isarranged to control the variable-period activation module.

In a second embodiment the timer is mounted in the microprocessor (4)and is arranged to be controlled by the fixed-period activation module.

Other features and advantages will become clearer in the detaileddescription herein under of two embodiments of the invention, made withreference to the attached drawing in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a functional block diagram of the first embodiment ofthe pressure sensor and of the microprocessor of the invention;

FIG. 2 illustrates a simplified block diagram of vehicle and wheelassembly lines on which sensors such as that of FIG. 1 are assembled and

FIG. 3 illustrates a diagram of a part of the functional blocks of thesecond embodiment of the pressure sensor and of the microprocessor ofthe invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the first embodiment of FIG. 1 the tire pressure sensor 20 isassociated with a power-supply battery 15, a measuring microprocessor 4,also powered by the battery 15 and able to take, by means of a pollingfunction 13, and to process, by means of a monitor 12, measurements ofphysical variables including the pressure of the tire Pr, the operatingtemperature .theta..sub.f and other indicative parameters relating tothe rotation of the wheel, for example the speed of rotation V.sub.r orthe centrifugal force F.sub.r. These physical variables are sensed by anassembly 2 of microsensors, respectively manometric membrane,thermistor, microgyroscope or microaccelerometer or rolling switch. Themonitor 12 of the microprocessor 4 controls a radio transmission circuit5 to communicate, to the vehicle's on-board computer 30, in operatingtime, the identification ID of the sensor, the measurements collectedand possibly certain results of the processing carried out, these databeing organized in a predetermined frame in order to be transmitted.

An activation module 3 in the pressure sensor 20 connected to themicroprocessor 4 by a connection 9 initiates operation of thismicroprocessor in a cyclical manner with a period T imposed by anactivation control timer 6 mounted in the sensor 20 connected to theactivation module 3 by a connection 10. The period T is calculated by atiming function 7 of the microprocessor 4 in order to program the timer6 via a connection 8. In the proposed exemplified embodiment thefunction 7 forms part of the microprocessor 4. The activation module 3also receives information on the pressure and/or rotation of the wheelfrom the microsensor assembly 2.

From the polling function 13 and by means of the monitor 12 the timingfunction 7 receives the values of the physical variables it requires tocalculate the period T to be imposed on the activation module.

The organization of the wheel and vehicle assembly lines should now bediscussed.

With reference to FIG. 2 the vehicle assembly line 100 includes thevehicle of the number or row V of the line. In a parallel manner on thewheel assembly line 200 the wheels of the vehicle V are assembled, thesuccessive numbers or rows Pi=Po+i of which (i being an integer from 0to 4) in the line are in a biunique relationship with the number V ofthe vehicle on which they will be assembled at the station 101. Forexample the first wheel assembled on the vehicle V is such that:Po=5×V−4the integer i being an indicator of the location L of the wheel Po+i onthe vehicle V.

For example it is possible to consider that i=1 if the wheel is locatedat the front left of the vehicle, that i=0 if it is the spare wheel,etc. . . .

In other words in this example it is possible to deduce from theposition Pi of the wheel on the wheel assembly line its allocation tothe vehicle V, its location L on the vehicle V of the vehicle assemblyline by calculating the integer i as follows:

$\begin{matrix}\left. \begin{matrix}{i = {{Pi} - {5 \times V} + 4}} \\{{{with}\mspace{14mu} O} \leq i \leq 4}\end{matrix} \right\} & (1)\end{matrix}$

Thus on the wheel assembly line, after a step 201 of mounting thepressure sensors and a step 202 of mounting the tires on the wheel rims,the process passes to an inflation step 203 and a wheel-balancing step204. These operations are very quick. Thus the balancing only takes afew seconds. During this latter wheel-balancing step, the number Pi ofthe wheel and the identification number IDp of the wheel pressure sensorare sensed, this latter being sensed by a receiver 214 in the mannerexplained below. These two parameters are transmitted to a diagnosticstation 103 which registers that the wheel Pi is fitted with a pressuresensor with the identification IDp. When the vehicle no. V, at a step102, arrives at the diagnostic station 103 for teaching of its on-boardcomputer, the station 103 deduces that the vehicle V is fitted withwheels Pi=5 V−4+i with 0≦i≦4 (2) of identification IDp and location Lcorresponding to the integer i.

The operation of the pressure sensor 20, from the time of itsinstallation on the wheel assembly line until its current usage, willnow be described.

At the start of the wheel assembly line the battery 15 powers theelectronic elements but they are in a so-called storage mode and thecurrent consumed is very low (less than 100 nA). In the storage mode thesensor activates the microprocessor after a specific period in order forit to read the pressure value, validate the mode and return to thedormant mode. In this mode the transmission circuit is always in dormantmode.

Storage mode is maintained as long as the microprocessor 4 does notdetect a pressure difference. Under the action of a pressuremicrosensor, typically a manometric membrane of the assembly 2, if thepressure exceeds a certain threshold (in this case 0.7 bar) there is atransition from the storage mode to the parking mode and the systembecomes active. In parking mode the activation period can be, forexample, one hour. Incidentally, it will be noted that in driving mode(road) the period can be one minute.

In a predetermined step of the wheel assembly line it is possibleautomatically to transmit to the vehicle assembly line 100 the positionPi of the wheel on which the pressure sensor is mounted.

The predetermined step of the wheel assembly line which is of relevancein this case can be the step 203 for pressurizing the tire (inflation)or preferably the wheel-balancing step 204. In this step the activationperiod can be very short (for example 1 s). Depending on the case theinformation from the pressure microsensor Pr (manometric membrane) orrotation microsensor (microgryo) Vr or even the centrifugal force sensorFr (rolling switch, microaccelerometer) is transmitted to the activationmodule 3 by the connection 11 from the microsensor assembly 2, whichcauses the microprocessor 4 to be activated via the connection 9. Theconnections 8, 9, 10 may conform to the protocol SPI (SynchronousProtocol Interface). The monitor 12 of the microprocessor initiates thepolling function 13 and receives the measurements P.sub.r,.theta..sub.f, V.sub.r therefrom which it transmits to the timingfunction 7 in order to program the timer 6.

The timing function 7 checks the content of the memory 14. If thiscontent corresponds to its storage mode then assembly is taking placeand the timing function 7 communicates to the timer 6 a period T₁ oftransmission of the predetermined frame containing, in particular, theidentification number ID of the sensor compatible with the assembly rateof the assembly lines, stores in memory 14 the new state of operation ofthe sensor corresponding to the assembly phase, then returns themicroprocessor 4 to its dormant state.

The timer 6 subsequently activates the activation module 3 in the periodT₁ in order to activate the microprocessor 4 which, taking account ofthe state of the memory 14 and by means of the monitor 12, controls thetransmission circuit 5 to transmit the predetermined frame, then returnsto its dormant state.

The period T.sub.1 is very short, of the order of a few tens of seconds,and the corresponding frames 204 are, for example, transmitted duringthe period covering the time in which the wheel balancing step iscarried out on the wheel assembly line, so as to avoid any ambiguitywith the wheels which precede or follow in the assembly line. At thewheel-balancing station 204 processing the wheel at position P in thewheel assembly line 200 a radio receiver 214 is provided receiving thepredetermined frame transmitted by the pressure sensor of the wheel Pand containing, in particular, the identification IDp of the saidsensor. The radio receiver 214 produces a message containing the data Pand IDp which it communicates to the diagnostic station 103 responsiblefor teaching the on-board computer of the vehicles of row V on thevehicle assembly line 100. For each vehicle V the diagnostic station 103deduces which wheels P are to be fitted to it, for example, by theformulae (2) and to which location L these wheels P of sensor IDp areallocated, for example, by the formulae (1). The radio receiver 214initializes the diagnostic station 103 which will program the on-boardcomputer of the vehicle V when this vehicle is at the teaching station102.

The interval from the time of transmission of the frame to the period T₁can be determined by detecting the rotation of the wheel by the assembly2. The pressure sensor is then placed in its parking mode by themicroprocessor 4, the timer being adjusted to a period T₂ of about onehour.

When the vehicle is in current use, this parking mode is interruptedwhen the wheel is caused to rotate again, the process remains the samebut the state of the memory 14 shows that assembly is no longer takingplace and the timing function 7 calculates a period T₂ which this timeis not a predetermined period but which depends on measurementscollected by the polling function 13, principally the temperature θ_(f)of the tire.

For a normal temperature θ_(f) the period T₂ is fixed at a few seconds.

If the temperature θ_(f) becomes excessive, for example, because ofheating of the tires as a result of repeated braking, the period T₂ canbe changed to close to 2000 seconds. It will be clear that thetemperature may fall again during this time. For this reason it may beadvantageous to activate the microprocessor prematurely and to activatethe timing function 7 in order to modify the activation period. To thisend the activation module 3 is sensitive to a gradient in thetemperature θ_(f) by the connection 11 and activates the microprocessor4 if the temperature θ_(f) varies by a certain percentage in theduration of a period T₂.

An embodiment is described above in which the activation control timer 6was located in the pressure sensor, outside the microprocessor 4, andcould be programmed by the microprocessor 4, the activation module 3being controlled by the programmable timer 6 to periodically activatethe microprocessor following a variable period.

In another embodiment, of which only the elements which distinguish itfrom the first will be described with reference to FIG. 3, theactivation module 3′ in this case has a fixed period T (for example, onesecond). The activation control timer 6′ is located inside themicroprocessor 4. It is still a timer which can be programmed by thetiming function 7 of the microprocessor but it is the activation module3′ which controls it in order that, via its output 61, it periodicallyactivates the microprocessor 4 following a variable period P, beingvariable, for example, from 1 second to 2000 seconds, or 65536 seconds,if it is a 2¹⁶ bit timer. Thus if the period of the activation module 3′is 1 s, the pressure sensor will increment the timer 6′ by one unit foreach second and, if the timing function 7 has been “programmed to 8” forexample, the activation of the microprocessor will take place everyeight seconds, i.e. every eight pulses of the activation module. Thetimer 6′ in this case acts as a frequency divider (period multiplier).

It will be noted that in the case of this second embodiment themicrosensors 2 are not connected to the activation module 3′.

1. An assembly, comprising: a tire pressure sensor for automobilevehicle wheels; and a microprocessor for pressure measurement and forcontrol of a radio transmission circuit, wherein the tire pressuresensor has an activation control timer and a module for activating themicroprocessor that is associated with the activation control timer,wherein the activation control timer is programmable, and wherein themicroprocessor is arranged to program the activation control timer. 2.The assembly of claim 1, wherein the microprocessor for programming theactivation control timer is sensitive to a temperature of a tire.
 3. Theassembly of claim 1, wherein the microprocessor for programming theactivation control timer is sensitive to a pressure of a tire.
 4. Theassembly of claim 1, wherein the microprocessor for programming theactivation control timer is sensitive to at least one of a speed ofrotation and to a centrifugal force caused by rotation of acorresponding wheel.
 5. The assembly of claim 4, further comprising aradio transmission circuit controlled by the microprocessor, wherein theradio transmission circuit is arranged to transmit informationcontaining at least an identification of the sensor at an acceleratedrate during balancing of the corresponding wheel being assembled and ata slowed rate when a temperature of the corresponding wheel increases.6. The assembly of claim 1, wherein the activation control timer ismounted in the pressure sensor and is arranged to control avariable-period activation module.
 7. The assembly of claim 1, whereinthe activation control timer is mounted in the microprocessor and isarranged to be controlled by a fixed-period activation module.
 8. Apressure assembly for use with a wheel of a motor vehicle, the assemblycomprising: a tire pressure sensor; and a processing circuit configuredto receive signals from the tire pressure sensor and output data basedon the tire pressure, the processing circuit having a periodicoperation; wherein a period of the periodic operation of the processingcircuit is variable and comprises a predetermined finite period of timewhich can be interrupted by occurrence of a predetermined event causingthe processing circuit to operate.
 9. The assembly of claim 8, whereinthe predetermined event is determined based on a gradient intemperature.
 10. The assembly of claim 8, wherein the processing circuitis configured to be controlled to operate at a first rate when atemperature is at a first value and is configured to be controlled tooperate at second rate slower than the first rate when the temperatureis at a second value higher than the first value.
 11. The assembly ofclaim 10, wherein the processing circuit is configured to be controlledsuch that when operating at the second rate, the processing circuit isinterrupted and will activate upon the occurrence of the predeterminedevent.
 12. A method for operating a tire pressure sensor assembly of amotor vehicle configured to monitor pressure of a tire of the vehicle,comprising: operating a microprocessor of the tire pressure sensor at afirst rate greater than zero; and operating the microprocessor at asecond rate greater than zero in response to a signal received from asensor that is configured to monitor a parameter of an environment ofthe tire, the second rate being different than the first rate.
 13. Themethod of claim 12, wherein the second rate is slower than the firstrate.
 14. The method of claim 12, wherein the parameter of the tire is atemperature of the tire.
 15. The method of claim 12, wherein operatingthe microprocessor comprises controlling the microprocessor with atimer.
 16. The method of claim 15, wherein the timer is programmablebased on data received from the sensor.
 17. The method of claim 12,further comprising operating the microprocessor at a third rate greaterthan zero in response to a signal received from a second sensor that isconfigured to monitor a parameter related to the tire, the third ratebeing different than the first rate and the second rate.